As I mention in my book, N acetyl cysteine (NAC) is not found in food sources, but in the body, it converts into cysteine. NAC acts as a precursor to glutathione, a powerful N Acetylcysteine and Probenecid Adjuvant Therapy for Traumatic Brain Injury Neurotherapeutics Springer Nature Link The Yack on NAC (N Acetyl Cysteine) and Parkinson's Journey with Parkinson's Acetaminophen Pathway (toxic doses), Pharmacokinetics